1106 Parsing A Boolean Expression 解析布尔表达式
Description:
Return the result of evaluating a given boolean expression, represented as a string.
An expression can either be:
"t", evaluating to True;
"f", evaluating to False;
"!(expr)", evaluating to the logical NOT of the inner expression expr;
"&(expr1,expr2,...)", evaluating to the logical AND of 2 or more inner expressions expr1, expr2, ...;
"|(expr1,expr2,...)", evaluating to the logical OR of 2 or more inner expressions expr1, expr2, ...
Example:
Example 1:
Input: expression = "!(f)"
Output: true
Example 2:
Input: expression = "|(f,t)"
Output: true
Example 3:
Input: expression = "&(t,f)"
Output: false
Constraints:
1 <= expression.length <= 2 * 10^4
expression[i] consists of characters in {'(', ')', '&', '|', '!', 't', 'f', ','}.
expression is a valid expression representing a boolean, as given in the description.
题目描述:
给你一个以字符串形式表述的 布尔表达式(boolean) expression,返回该式的运算结果。
有效的表达式需遵循以下约定:
"t",运算结果为 True
"f",运算结果为 False
"!(expr)",运算过程为对内部表达式 expr 进行逻辑 非的运算(NOT)
"&(expr1,expr2,...)",运算过程为对 2 个或以上内部表达式 expr1, expr2, ... 进行逻辑 与的运算(AND)
"|(expr1,expr2,...)",运算过程为对 2 个或以上内部表达式 expr1, expr2, ... 进行逻辑 或的运算(OR)
示例 :
示例 1:
输入:expression = "!(f)"
输出:true
示例 2:
输入:expression = "|(f,t)"
输出:true
示例 3:
输入:expression = "&(t,f)"
输出:false
示例 4:
输入:expression = "|(&(t,f,t),!(t))"
输出:false
提示:
1 <= expression.length <= 20000
expression[i] 由 {'(', ')', '&', '|', '!', 't', 'f', ','} 中的字符组成。
expression 是以上述形式给出的有效表达式,表示一个布尔值。
思路:
- 栈
使用两个栈, 一个栈记录操作, 另一个栈记录操作数(true, false)
遍历 expression, 将操作数和操作压入栈直到遇到右括号
按照不同的操作给出当前操作的结果并存入操作数栈
最后得到的操作数栈顶即为结果
时间复杂度O(n), 空间复杂度O(n) - 递归
每次遇到 '|' 或者 '&' 进入递归处理
其他正常遍历即可
时间复杂度O(n), 空间复杂度O(n)
代码:
C++:
class Solution
{
public:
bool parseBoolExpr(string expression)
{
const char *e = expression.c_str();
return parse(e, &e);
}
private:
bool parse(const char *e, const char **p)
{
bool result;
*p = e + 1;
if (*e == '!')
{
result = !parse(*p + 1, p);
++*p;
return result;
}
if (*e == 'f') return false;
if (*e == 't') return true;
result = (*e == '|' ? false : true);
do
{
if (*e == '|') result = parse(*p + 1, p) or result;
else result = parse(*p + 1, p) and result;
} while (**p != ')');
++*p;
return result;
}
};
Java:
class Solution {
public boolean parseBoolExpr(String expression) {
Deque<Character> operands = new LinkedList<>(), operators = new LinkedList<>();
for (char c :expression.toCharArray()) {
if ('t' == c || 'f' == c || '(' == c) operands.push(c);
else if ('|' == c || '&' == c || '!' == c) operators.push(c);
else if (')' == c) {
char operator = operators.pop();
boolean result = '&' == operator;
while (!operands.isEmpty()) {
char operand = operands.pop();
if ('(' == operand) break;
else if ('&' == operator) result &= (operand == 't');
else if ('|' == operator) result |= (operand == 't');
else result = operand == 'f';
}
operands.push(result ? 't' : 'f');
}
}
return operands.pop() == 't';
}
}
Python:
class Solution:
def parseBoolExpr(self, expression: str) -> bool:
return eval(expression.replace('f', '0').replace('t', '1').replace('!', 'not |').replace('&(', 'all([').replace('|(', 'any([').replace(')', '])'))
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